The ultimate purpose of this research is to reveal the physiological bases for differential reflex changes in activity of renal and splenic sympathetic nerves which potentially contribute to complex cardiovascular adjustments in behaving animals or man. The kidney and spleen are highly vascular abdominal organs involved in cardiac vascular homeostasis which receive innervation from the same ganglia and spinal cord segments. These facts, as well as early concepts of mass activation of sympathetic outflow, suggest that the kidney and spleen would receive identical neural influences. Although the capacity of the sympathetic nervous system to discharge differentially has been recognized recently, outflow to the viscera generally has been considered collectively. However, previous investigations in this laboratory have illustrated selective, differential, (even opposite) reflex influences on renal and splenic nerves. The objective of this research is to investigate renal and splenic sympathetic responses to afferent inputs from visceral and skeletal muscle receptors in anesthetized cats. Receptors will be stimulated in a manner which can be related to conditions known to occur naturally, i.e., by organ congestion, by noxious substances, by urine hyperosmolarity or obstruction or by models of skeletal muscle exercise. Reflexes will be compared with and without the buffering influences of arterial baroreceptors and vagal afferent nerves. Multifiber and single fiber electrophysiological techniques will be employed to identify response characteristics within renal and splenic populations of neurons. The extent to which splenic nerve responses typify splanchnic visceral outflow will be assessed. Responses of the kidney and spleen caused by "differential" renal and splenic sympathetic reflexes will be assessed to determine if selective neural responses are translated to selective target organ responses. Responses of spinal preganglionic neurons will be evaluated to identify possible renal-like and splenic-like neurons in the CNS. Identification of such neurons would suggest that the innervation of specific visceral organs is dedicated within the spinal cord. Sympathetic influences on viscera such as the kidney and spleen may be more discretely organized than has been considered previously, and this fine control could contribute significantly to complex cardiovascular adjustments required for homeostasis.